How much current can 12 AWG copper wire carry?

Per NEC Table 310.16, 12 AWG copper is rated 25 amps at 75°C and 30 amps at 90°C, but residential branch circuits with 12 AWG are limited to 20 amp breakers under NEC 240.4(D).

What is the difference between MCM and kcmil?

MCM and kcmil are the same unit: one thousand circular mils of conductor cross-section. MCM is the older abbreviation and kcmil is the modern one. 250 MCM and 250 kcmil describe identical conductors.

Is 250 MCM bigger than 4/0 AWG?

Yes. 250 MCM is 250,000 circular mils, while 4/0 AWG is 211,600 circular mils (about 212 MCM), so 250 MCM is roughly 18 percent larger in cross-section.

AWG to MCM Wire Gauge Chart

Every common wire size from 26 AWG through 1000 MCM with its MCM/kcmil equivalent, diameter, cross-section in circular mils and mm², DC resistance, and NEC copper ampacity. The complete American Wire Gauge conversion table.

AWG to MCM Conversion Table

Every AWG size has an exact MCM (kcmil) equivalent: divide the area in circular mils by 1,000. The MCM Equivalent column below lets you convert in either direction at a glance. AWG sizing ends at 4/0 (211.6 MCM); everything larger is specified directly in MCM.

Size	MCM Equivalent (kcmil)	Area (cmil)	Area (mm²)	Diameter (in)	Diameter (mm)	DC Resistance (Ω/1000 ft)*	Ampacity 75°C / 90°C†
26 AWG	0.254	254	0.129	0.0159	0.405	40.8	N/A
24 AWG	0.404	404	0.205	0.0201	0.511	25.7	N/A
22 AWG	0.642	642	0.326	0.0253	0.644	16.1	N/A
20 AWG	1.02	1,020	0.518	0.0320	0.812	10.2	N/A
18 AWG	1.62	1,620	0.823	0.0403	1.02	6.51	N/A
16 AWG	2.58	2,580	1.31	0.0508	1.29	4.09	N/A
14 AWG	4.11	4,110	2.08	0.0641	1.63	2.57	20 / 25 A
12 AWG	6.53	6,530	3.31	0.0808	2.05	1.62	25 / 30 A
10 AWG	10.4	10,380	5.26	0.1019	2.59	1.02	35 / 40 A
8 AWG	16.5	16,510	8.37	0.1285	3.26	0.641	50 / 55 A
6 AWG	26.2	26,240	13.3	0.1620	4.11	0.403	65 / 75 A
4 AWG	41.7	41,740	21.2	0.2043	5.19	0.253	85 / 95 A
3 AWG	52.6	52,620	26.7	0.2294	5.83	0.201	100 / 115 A
2 AWG	66.4	66,360	33.6	0.2576	6.54	0.159	115 / 130 A
1 AWG	83.7	83,690	42.4	0.2893	7.35	0.126	130 / 145 A
1/0 AWG	106	105,600	53.5	0.3249	8.25	0.100	150 / 170 A
2/0 AWG	133	133,100	67.4	0.3648	9.27	0.0795	175 / 195 A
3/0 AWG	168	167,800	85.0	0.4096	10.40	0.0630	200 / 225 A
4/0 AWG	212	211,600	107	0.4600	11.68	0.0500	230 / 260 A
250 MCM	250	250,000	127	0.5000	12.70	0.0423	255 / 290 A
300 MCM	300	300,000	152	0.5477	13.91	0.0353	285 / 320 A
350 MCM	350	350,000	177	0.5916	15.03	0.0302	310 / 350 A
400 MCM	400	400,000	203	0.6325	16.06	0.0264	335 / 380 A
500 MCM	500	500,000	253	0.7071	17.96	0.0212	380 / 430 A
600 MCM	600	600,000	304	0.7746	19.67	0.0176	420 / 475 A
750 MCM	750	750,000	380	0.8660	22.00	0.0141	475 / 535 A
1000 MCM	1000	1,000,000	507	1.0000	25.40	0.0106	545 / 615 A

*Approximate DC resistance of uncoated solid copper at 20°C. Stranded and coated conductors read slightly higher. †Copper conductor ampacity per NEC Table 310.16 (not more than three current-carrying conductors in raceway, 30°C ambient). Small-conductor rules in NEC 240.4(D) cap overcurrent protection at 15 A for 14 AWG, 20 A for 12 AWG, and 30 A for 10 AWG copper. This chart is for reference only; verify against the NEC for your installation.

The Aught Sizes: Where AWG Meets MCM

The four "aught" sizes bridge the gap between numbered AWG sizes and MCM. They're written with slashes and read as "one-aught" through "four-aught":

Aught Size	Also Written	MCM Equivalent
1/0 AWG ("one-aught")	0	106 MCM
2/0 AWG ("two-aught")	00	133 MCM
3/0 AWG ("three-aught")	000	168 MCM
4/0 AWG ("four-aught")	0000	212 MCM

After 4/0, the next standard conductor size jumps to 250 MCM, which is why you'll never see a "5/0" cable on a spec sheet.

How AWG Works

American Wire Gauge runs backwards from what most people expect: the smaller the number, the bigger the wire. Each 3-gauge step doubles the cross-sectional area (and roughly halves the resistance), and each 6-gauge step doubles the diameter. Above 4/0 AWG ("four-aught"), sizes switch to MCM/kcmil, which measure thousands of circular mils of cross-section.

Converting between the two systems is simple: MCM = circular mils ÷ 1,000. A circular mil is the area of a circle one mil (0.001") in diameter, so a conductor's circular-mil area equals its diameter in mils squared. That's why a bare 500 MCM conductor measures about 0.707" across: 707 mils squared is 500,000 circular mils.

Two numbers on this chart drive nearly every wire-sizing decision: ampacity (how much current the conductor can safely carry) and resistance (how much voltage you lose over distance). For short runs, ampacity usually governs. For long runs, voltage drop takes over. Use our wire size calculator to check both at once.